This invention relates in general to a method of producing a thin film capacitor having a tantalum thin film electrode mounted on an electrically nonconducting support.
A thin film capacitor has become known (West German Offenlegenschrift 1,589,060) wherein a film of .beta.-tantalum is deposited on a hard-glass plate. The film forms the base electrode to which are connected a dielectric of tantalum pentoxide (Ta.sub.2 0.sub.5) and an opposing electrode of gold.
Experiments have shown (J. Electrochem. Society, Vol. 119, No. 9, page 1215 ff, Schoen) that these capacitors have only a low thermal rating. The characteristics relevant to capacitors such as capacitance (C), temperature coefficient of the capacitance (C.sub.c) and leakage (tan .delta.) increase appreciably with heating, more particularly at temperatures above 200.degree. C. However, new technological processes such as inexpensive dip soldering for contact making cannot be employed for these capacitors, since any momentary heating to high temperatures must be avoided. Furthermore, artifical aging at a sufficiently high temperature so as to achieve an ideal life characteristic is not possible.
A method is likewise known using tantalum nitride (Ta.sub.2 N) for the base electrode of such capacitors (Gerstenberg, Journal of the Electrochemical Society, June 1966, page 542 ff). These experiments show that with Ta.sub.2 N as primary material and increasing the temperature (110.degree. C) or the voltage (.ltoreq. 750 volts in the case of a 225 volt anodizing voltage) the durability of the capacitor is better than that of a .beta.-tantalum capacitor.
Accordingly, it is an object of this invention to provide a method of production which will have the effect of improving the characteristic properties of thin film capacitors in such a way that the capacitors can be used in a wide range of applications, where they will experience a wide range of ambient conditions.